In devices adapted to perform two kinds of work, i.e., to fasten and loosen bolts and nuts, the change of direction of rotation from forward fastening rotation to reverse loosening rotation and vice versa is almost always effected by changing the direction of rotation of the motor itself.
Electric or pneumatic motors, which are generally used for fastening-loosening devices for bolts and nuts, include reversible motors and those rotatable in only one direction (nonreversible motors). When these two types of motors are compared on the basis of the same output level, the former is 20 to 30% larger than the latter and is also heavier. Nevertheless, reversible motors are used in almost all cases because this type of motors can be changed over in the direction of rotation only by manipulating a switch, hence a simplified construction.
The fastening-loosening device for bolts and nuts is heavy, imposes a great burden on the worker when used for a long period of time and therefore has a major problem in that the device must be reduced in weight.
As previously stated, the reversible motor is greater in size than the nonreversible motor at the same output level. Accordingly, use of the nonreversible motor is advantageous for reducing the weight of the device insofar as motors only are concerned.
When the nonreversible motor is to be incorporated into fastening-loosening devices, however, there arises a need to use a mechanism which permits forward and reverse rotations with the same characteristics and exhibits the same transmission efficiency for forward and reverse rotations.
Conventionally available as means fulfilling these requirements is a rotation changing assembly wherein bevel gears are used. This assembly comprises two driven bevel gears slidably arranged as opposed to each other on a common axis orthogonal to the axis of a drive bevel gear coupled to a motor. One of the driven bevel gears is selectively meshed with the drive gear for transmitting a torque to a socket mechanism via the driven gear and a planetary gear mechanism.
For either one of the driven bevel gears to be selectively engaged with and disengaged from the drive bevel gear, the above bevel gear assembly needs to have a mechanism for slidingly driving the driven bevel gear which mechanism is disposed outside the bevel gears. The casing of the fastening-loosening device then becomes increased in size to provide a space for accommodating the mechanism and a space for permitting the sliding movement of the driven bevel gear. The increase in the size of the casing and the weight of the mechanism for slidingly driving the bevel gear inevitably increase the size and weight of the entire device although the nonreversible motor is used.
The present invention provides a device for fastening and loosening threaded members wherein one of a pair of driven bevel gears which are in mesh with a drive gear at all times is selectively engageable with an output shaft for a change-over to forward rotation or to reverse rotation so as to lessen the increase of size and weight.